It is known in the prior art that the frequency of light waves can be captured in silver halide photographic emulsion in the form of vertically embedded standing waves, with the wave's nodal points physically representing its frequency. In 1908 Gabriel Lippmann won the Nobel Prize in Physics “for his method of reproducing colours photographically based on the phenomenon of interference” (quote from the Presentation Speech by Professor K. B. Hassel berg, President of the Royal Swedish Academy of Sciences, on Dec. 10, 1908). This specific technique was first described in 1891 to store and extract color information from specially constructed monochromatic photographic plates (Lippmann, G, “La Photographic des Couleurs,” Compte Rendes a l'Academie des Sciences, Tome 112, pp 247-275, February 1891). While never commercialized successfully because of the difficulties of viewing the color image, reproducing the image beyond its first iteration on a glass plate, and the rudimentary, extremely slow photographic chemistry at the time, the Lippmann process is applied in the present invention in a novel methodology and apparatus for the storage of digital data as well as human-readable images and text, as described herein.
The Lippmann process works as follows: the lightwave color palette contains the information in the form of a ray representing the specific colors. This forward ray (entering through the transparent side of the storage medium) traverses the emulsion and is reflected back from a reflecting layer (in Lippmann's specific case the reflective layer was a pool of liquid mercury. As the reflected light wave returns through the emulsion it combines with the forward wave, causing interference. This interference results in cancellation of the light at opposing wave nodes and reinforcement at the in-phase nodes. Thus, vertically through the emulsion, there are regularly spaced areas of exposure (where the waves reinforce), followed by areas of zero exposure where the waves cancel.
The Lippmann silver grains as exposed (and developed) are embedded in successive laminae coinciding with the anti-nodal planes of the standing waves recorded, equal to the half-wavelength of the light that forms the waves. This is known in the art as a “Lippmann emulsion”—a relatively thin, transparent, and extremely fine-grained panchromatic photosensitive coating, as described further in excerpts from contemporary texts below. The spacing of the exposed vertical grains literally represents the wavelengths of the specific impinging light. For each color this spacing is, of course, different. A contemporary explanation and some history of the prior art is in Wood, R W, Physical Optics, Macmillan, 1934, pp 214-217, excerpted herein, especially the illustrations for the laminae, reproduced herein as prior art in FIGS. 6 and 7:                “Lippmann's Color Photographs. Photographs in natural color were accidentally obtained by E. Becquerel in 1850, by means of standing light-waves, although he was not aware of the part they played. In 1868 Zenker explained the colors, sometimes seen in Becquerel's photographs of the spectrum, as due to standing waves, formed by the reflection of the light from the surface of the silver plate on which the sensitive film was formed. The silver was reduced in the anti-nodal planes forming a system of reflecting laminae, which showed interference-colors in reflected light . . . .        “A process of direct color photography, based upon this principle, was originated by Lippmann in 1891. The photographic plate is placed in the camera with the glass side facing the objective, and the sensitive film backed by a reflecting layer of mercury. This of course requires a special form of plateholder.        “A system of stationary waves is formed in the film as shown in FIG. 136 [illustrated herein as FIG. 6, prior art], and the silver compound is acted upon only at the antinodes, which form planes parallel to the reflecting surface. On developing and fixing the plate in the usual manner, it is found that the film shows, in reflected light, brilliant colors, similar to the colors which illuminated it. The silver, instead of being reduced in a mass, uniformly distributed throughout the thickness of the film, is laid down in thin laminae, coinciding with the antinodal planes of the stationary light-waves. The distance between the laminae is equal to the half wave-length of the light which formed them, consequently they show the same color by interference in reflected light . . . .        “By cutting a section of the film and examining it with a microscope, the laminae thrown down by the standing light-waves can be seen and counted. It was found in this way that as many as 250 laminae could be formed, if the sensitizing dye was introduced into the emulsion and the plate developed with hydroquinone. In the case of bathed plates the sensitizing action only penetrated a short distance, and with pyrogallic acid development the developing action occurred chiefly near the surface, limiting the possible number of laminae. A microphotograph of a similar section by Mr. Senior is reproduced in FIG. 138 [illustrated herein as FIG. 7, prior art]. Neuhauss in 1898 was the first to make thin sections of the film and observe the laminae with the microscope. Since the distance between them is λ/2 they are at the limit of the resolving-power of the microscope, but the effective distance can be increased by cutting sections in an oblique direction, or by causing them to swell by the application of moisture as was done by Cajal.        “Neuhauss improved the color process by bleaching the pictures with bichloride of mercury; this treatment increases the transparency of the laminae without sensibly reducing their reflecting power, consequently a larger number are able to cooperate, as the incident light is able to penetrate to a greater depth.”        
Note that Wood indicates that the laminae, representing physically the actual wave lengths of light, are closer together than contemporary optical microscopes could resolve at the time. So to produce a microphotograph [e.g., FIG. 7, prior art for this invention] it was necessary to expand the emulsion, as per Neuhauss as cited. (Today such cross-sections can be observed using an electron microscope.) In one embodiment of this invention described below we apply a similar methodology and apparatus to alter the wavelengths of the diffraction gratings or standing waves in order to more readily detect their frequency.
In Lippmann's original process, the colors represented a mapping of the actual colors of a scene focused on the special emulsion by a conventional camera apparatus. A full-color image with the Lippmann process is reconstructed by shining a white light source at a critical angle reflected toward the viewer from the developed and fixed emulsion, with the vertical interference columns being observed as the true colors of the original by the human visual system. In contrast to the prior art, the present invention only needs to record a small region for each data constellation, plus on the same emulsion monochromatic photographs, or interference color images, and human readable text, and microtext, if needed for reference, indexing, or for future retrieval where the details of the process may have been forgotten. This invention's data storage location methodology therefore simplifies the writing and reading apparatus for the embodiments described herein.
The Lippmann emulsion is developed, as known in the art, using specified photographic chemistry for its ultra-fine grain processing. As noted in the excerpt from Wood (op. cit, pp 215-217) above, the development and bleaching process is aimed primarily at the surface of the emulsion so as to minimize the number of laminae (hence this invention's requirement for a thin emulsion), and to eliminate most of the silver, so as to increase “the transparency of the laminae without sensibly reducing their reflecting power . . . ” (as per Neuhauss, in Wood, op. cit., p. 217). (For additional prior art on modern development see Rich, C, “Lippmann Photographic Process Put to Practice”, SPIE v. 2688, Society of Photo-Optical Instrumentation Engineers, 1996, pp. 88-95; U.S. Pat. No. 4,202,695; and Bjelkhagen, H I, Silver-Halide Recording Materials for Holography and Their Processing, Springer, 1995, esp. ch. 2.2.2, pp. 37ff on the preparation and developing formulae for Lippmann emulsions.)
Further details of the Lippmann process are described in a more recent book by L. A Mannheim thusly:                “58. Diffraction Colour Systems. A prism is the usual way of splitting white light into its spectral components. An alternative method is to employ a diffraction grating, i.e. a grid of regularly spaced lines ruled into for instance the surface of a glass plate, or a series of regularly spaced layers within the depth of a film emulsion. If the spacing is of the order of the wavelength of light, interference effects result in the reflection of light of specific wavelengths when white light is directed at this diffracting arrangement. This action is analogous to the selective colour transmission of interference filters . . . . The colour seen depends on the exact spacing of the grating lines or planes. If such planes can be formed of silver deposits in an emulsion, we could have a system of colour reproduction involving only diffracted light and no dyes. The earliest colour photographic process to use this idea was the Lippmann process. It was carried out by exposing a panchromatic plate, the emulsion of which was almost transparent, with its emulsion surface in contact with a metallic mirror. This was achieved by building special dark slides which allowed mercury to be run in behind the plates in order to ensure optical contact between the emulsion and metallic reflecting surface. Light passed through the emulsion and was reflected back by the mercury surface, but the light on the return passage through the emulsion layer was out of phase with that on the first passage. Thus an interference was set up and this resulted in the emulsion layer being rendered developable where the peaks of the waves coincided. The distribution of the image through the thickness of the emulsion layer when the plate was developed, was therefore dependent on the wavelength of the exposing light at every point on the picture. The developed negative was backed up with a mirror and viewed by reflected light. When the plate was illuminated and viewed at the correct angle the picture was seen in full colour. At every point in the picture light of all wavelengths, other than those which gave rise to the image, was absorbed. Those wavelengths which could go through the image and, after reflection, come back through the image, gave the correct colour sensation. From a scientific point of view this is an extremely elegant process but in practice it is not very useful. Not only are the taking and viewing conditions critical but emulsions of sufficient transparency are very slow.” [Photography Theory and Practice, Amphoto, 1970, Vol I, Sect 58, emphasis added]        
The ability to store data using light is generally limited by the wavelength of light. This has recently been exemplified by the introduction of so-called “Blu-Ray” DVD recorders. The shorter wavelength of the blue light source nearly doubles the recording density and, thus, the playing time. However, the lifetimes of such media are relatively short, ranging from a few years to possibly a century or a bit more if extreme care is taken to preserve the media against environmental damage (Solomon, R J, et. al., “Write Once, Read Forever (WORF): Low-energy storage in perpetuity of high-density, multi-state data,” Archiving 2014 Final Program and Proceedings, Berlin, Society for Imaging Science and Technology, vol. 5, pp. 118-122).
In accelerated testing as known in the art, silver- or metallic-based photographic media have been estimated to last upwards of tens of thousands of years, without requiring special energy-intensive storage conditions—a true archival system for future generations (Wilhelm, H, “Long-Term Preservation of Photographic Originals and Digital Image Files . . . ”, IS&T's Archiving 2008 Conference in Bern, Switzerland, Jun. 26, 2008, Society for Imaging Science and Technology, p. 4). Specifically referring to the archival qualities of the modern application of the process, C. Rich (op. cit., p. 88) states that:                The Lippmann process . . . was the first stable direct color photographic process that derived it's color response from the recording of standing waves of light in the emulsion . . . . Using Bragg selectivity rather than absorbing dyes . . . , more than 100 years has proven a Lippmann type photograph's color stability [emphasis added, with “Bragg selectivity” implying detection of standing waves embedded as interference gratings].        